Analysis of fatigue crack propagation under mixed mode II plus III in ARMCO iron

Near-threshold propagation of shear cracks under mixed-mode II + III loading was investigated in ARMCO iron. Special specimens for simultaneous growth of cracks in II, III and II + III loading modes were employed in these experiments. All experiments were performed under small-scale yielding as verified by both analytical and numerical approaches. The most appropriate description of mixed-mode crack growth was found in terms of Delta a/Delta N vs. Delta K-eq dependences, where Delta K-eq = root Delta K-II(2) + beta . Delta K-III(2) and beta = 1.1. Also another mixed-mode criterion based on averaged using weight coefficients revealed to be useful. These analyses revealed that the mode III component of the mixed-mode loading was slightly less efficient for the mixed-mode crack-growth mechanism than that of the mode II which is in agreement with results reported for some other metallic materials. (C) 2014 Elsevier Ltd. All rights reserved.